Since Sony Corporation of Japan took the lead in development and commercialization of a lithium-ion battery in 1991, the lithium-ion battery has been rapidly developed and widely used. The lithium-ion battery has advantages of high operating voltage, high energy density, long cycle life, low self-discharge current, and having no memory effect. Thus, currently, the lithium-ion battery has become a preferred chemical power source of a high-grade consumer electronic product.
Currently, a negative electrode of the lithium-ion battery is usually made of a graphite material, because the graphite material has advantages of good reversibility of intercalation/deintercalation of lithium ions, low potential plateau and excellent charge-discharge cycle performance. However, the lithium ions passing in and out of a graphite layer must be from edges of the graphite layer, i.e. along a direction parallel to the graphite layer. A diffusion coefficient of the lithium ions passing in and out of the graphite layer is small, which severely restricts the high-rate charge-discharge performance of the lithium-ion battery. When the lithium-ion battery is charged-discharged at high current density, the lithium ions can not diffuse into the graphite interlayer of the negative electrode in time. The lithium ions will concentrate on the surface of the negative electrode and are reduced to an active metal lithium crystallite or a big lithium dendrite. The metal lithium crystallite is prone to react with an electrolyte of the lithium-ion battery to generate heat and gas, meanwhile lead to capacity reduction, thereby severely shortening the cycle life of the lithium-ion battery. The lithium dendrite may cause an internal short circuit of the lithium-ion battery, thereby bringing security risks.
Currently, the graphite material can be modified by a surface oxidation and reduction treatment, a doping treatment or a coating treatment. Chinese Patent No. CN 200610060814.X (Zhanjiang Juxin electronic material Co., Ltd., China) and Chinese Patent No. CN 200610061625.4 (Shenzhen Beiterui material Co., Ltd., China) disclose composite graphite particles formed by bonding natural graphite powder and artificial graphite powder together with an adhesive. The composite graphite particles include nanopores and sub-micron pores. The nanopores and sub-micron pores provide more channels for the lithium ions passing in and out of the graphite layer, thereby improving the cycling stability of the lithium-ion battery. Wu, Zhuangxiong (Chinese Patent No. CN 201010246172.9) discloses a method for preparing a graphite material with nanopores. In the method, an additive and a pore-forming agent are added into a coke and the graphite material is prepared at a high temperature (1600˜3000° C.). Although a certain amount of pores can be generated in the graphite material by using the method, the graphite material prepared by using the method still has big graphite crystals, and a ratio of an area of a graphite layer to an area of a graphite layer section perpendicular to the graphite layer is still too large. Thus, the graphite material can not be used at high current density.